Please refer to FIG. 1, which shows an embodiment for a typical flat bed optical scanner 1 seen in current market. Mainly, a document window glass is arranged on an upper side surface of the outer shell 11 of a scanner 1 to place a scanned document (not shown). An optical chassis 14, driven by a driving apparatus 13, proceeds a linear motion along the direction of a guiding rod 15 inside a hollow outer shell 11 to proceed an image-scanning job for the document on the glass 12.
Please refer to FIG. 2, which is an A—A sectional view for the optical chassis 14 of a prior optical scanner 1 in FIG. 1. The optical chassis 14 includes: a hollow shell body 141, a light source 142, which is positioned at an appropriate position on the upper side plane of the shell body 141, a light-guiding apparatus, which is assembled by plural reflection mirrors 143, a lens set 144, and a charge-coupled device 145. The light source 142 emits a light to the document (not shown), and its reflection light enters into the interior of the shell body 141 of the optical chassis 14 and is reflected by the plural reflection mirrors 143 in the light-guiding apparatus to lengthen its optical length to an appropriate length. Afterwards, the reflected light is focused by the lens set 144 and formed into an image on the charge-coupled device 145, by which the scanned image data is converted into electronic signals.
Please refer to FIG. 1 and FIG. 2, which show the prior optical chassis 14. Because the reflection mirror 143 is constructed by plating silver on a thin-plate-typed glass that is unable to be directly piled-up and positioned by itself, so  additional spring pieces 146, a fixture mechanism, or a method of matching screw locking are needed to fix the reflection mirror 143 at predetermined position inside the shell body 141. Not only the  The positioning elements of additional spring pieces 146 and fixture mechanism would  directly cause the  an increase of parts number and production cost and raise the assembly time and manpower cost, . but also  Additionally, even if plenty number  of assembly parts is  existed, then the occupying volume is caused to increase  must be increased, and it is unavoidable to happen the situation that  the parts loose  may loosen or create uneven holding strength would cause  causing position bias for the reflection mirror 143 and lower down  decrease the quality of image scanning. Furthermore, because  the spring pieces 146 would reduce its holding force due to the elasticity fatigue of the spring pieces 146 caused by long-period use would reduce its holding force  or under  caused by the vibration situations happened  experienced during machine transportation, . Likewise, the prior arts  that employs the spring pieces 145 as fixture mechanism for holding the reflection mirror 143 may also occur  experience the situations of loosening or position bias in the reflection mirror 143 and cause the quality lowering-down  decrease in image scanning and that is needed to be improved .
Furthermore, there is still one big shortcoming in the light-guiding apparatus of the prior optical chassis 14 shown in FIG. 1 and FIG. 2; namely, since each piece of reflection mirror has only one reflection plane to proceed single reflection for the light, and  in order to reach the total track (abbreviated as TT value, which is the total value of Y1+Y2 . . .+Y5 as shown in FIG. 2) needed by the lens set 144 to focus image clearly, so  the distance between each reflection mirror 143 is needed to be elongated (i.e. an increase in the values of Y2 and Y3), or the light is reflected twice on one reflection mirror, or an additional number of reflection mirrors are is  needed to increase for increasing  the times of reflection. However, the elongation of distance between each reflection mirror 143 would directly cause the enlargement of the total volume of the optical chassis 14. Twice reflections proceeded on one single mirror would cause the area increase for the reflection mirror or raise the complexity on the designs of light-path routes. And, the increase of the number of reflection mirrors would then cause the raise for  increase in both difficulty and cost in element assembly and mirror positioning for the optical chassis 14. All these arrangements are not the perfect solution methods.
Additionally, for all the optical chassis light-guiding apparatus in the optical chassis  seen in current markets, its  the reflection mirror 143 all is reflection mirror  are of thin-plate-shaped glass, neither each  no reflection mirror 143 is of modularized design, nor can it be inter-piled-up or positioned, while additional designs for positioning devices is  are needed to position the inter-angles and distances between each reflection mirrors 143. Not only would any errors on any position angle would  cause the lowering-down  a decrease of scanning quality, but also for the needs of different resolution, different outer sizes of optical chassis, different scanning paper sizes (the sizes of A3 or A4), or other needs for different light-path routes or total track of optical chassis, a set of position device is designed from the beginning to change the inter-position between each reflection mirror 143, and the usage is very inefficient.